Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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486 FXUS61 KPHI 232103 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 403 PM EST Mon Jan 23 2017 .SYNOPSIS... Strong low pressure near the Virginia Capes late today will drift northeast toward Long Island through Tuesday morning, before passing east of Cape Cod Tuesday evening. Weak high pressure crosses our region on Wednesday. A cold front passes southeastward off the mid Atlantic coast Thursday and with another cold frontal passage possible again Sunday or next Monday. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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Low pressure near the North Carolina coast will strengthen this evening as it moves offshore, then moves northeastward and offshore of the New Jersey coast tonight. The mid level low will pass to our south through the overnight and continue to send several vorticity impulses across the area through tonight. This will lead to periods of precipitation moving across the area. Most of the precipitation will fall as rain with some sleet mixing in just north and west of I-95. The exception to this will be Carbon and Monroe, Pennsylvania and Sussex, New Jersey. Portions of these counties, especially higher elevations are expected to be below freezing through tonight. So a wintry mix is expected across portions of these counties, especially the higher elevations. The question becomes how much of each P-Type falls across the area. Forecast thermal profiles vary through the night and we could give a period of each, freezing rain, sleet, and snow. We are expecting 2-5 inches of snow/sleet combination as well as up to one to two tenths of an inch of freezing rain. So we have kept the Winter Weather Advisory in place and as is for now. It is possible that more sleet could fall, which would make the snow and ice amounts less than forecast. Generally 1 to 2 inches of storm total QPF are forecast for much of the area, with portions of the Delmarva and southern New Jersey seeing the least, while portions of northeast New Jersey seeing the most. We continue with the Flood Watch for northeastern New Jersey which has 1.5 to 2 inches QPF, and isolated higher amounts possible. We have extended the High Wind Warning and Wind Advisory a few hours into this evening as winds continue to be gusty. Winds are expected to diminish some through the night, but will remain gusty at times, between 25-35 mph.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
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The coastal low will slowly drift to the east northeast during the day Tuesday. As the low moves away from the area, we could get some wrap around moisture across the area which could keep some light precipitation through the day. Current forecast temperatures would keep everything rain for most areas, except where the Winter Weather Advisory is in effect. If temperatures do not rise much during the day, it is possible that some areas could see snow or sleet mix in at times with any rainfall that occurs. For the areas under the Winter Weather Advisory, they have the better chance of seeing a winter mix into the day. For now, we will keep the end time of noon time, but this may need to be extended in time in the future. Winds will become northwesterly as the low moves to farther to our east and will remain gusty through the day with gusts around 20-25 mph expected.
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&& .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... 500 MB: Weak ridging follows the departure of our coastal storm Tuesday night and Wednesday, followed by a series of short waves that carves out a positive tilt trough in the eastern USA. Temperatures: around 10 degree above normal Wednesday, 10 to 15 above normal Thursday, 5 to 10 above normal Friday, cooling to near normal Sunday and Monday. Forecast basis: Unless otherwise noted, a 50 50 blend of the 12z/23 GFS/NAM MOS guidance Tuesday night-Wednesday night, thereafter the 12z/23 GFS MEXMOS Thursday and Thursday night, and then the 15z/23 WPC guidance Friday-Monday, at times blended with the 12z/23 GFS MEXMOS guidance or the long term temps were adjusted because of the 12z/23 ECMWF 18z 2m temperatures. The dailies... Tuesday night and Wednesday: a little leftover mixed precipitation is possible but it should not last long, if there is any. Conditions dry out Tuesday night as high pressure builds into the region and moves offshore during the day Wednesday. Gusty northwest winds to 20 or 25 mph Tuesday night and Wednesday morning become west or southwest Wednesday afternoon and diminish a bit. Wednesday night and Thursday...warm air advection ahead of cold front. Maybe a few showers. Lots of uncertainty regarding whether it will rain. Blended the MEX POPS with the previously drier forecast. Later Thursday into the weekend...gradual cool down with generally dry weather expected. Breezy at times. Next Monday...by then another cold front has either passed or is passing and the GFS is the first of our usual reviewed global models to suggest low pressure forming on the front over the mid Atlantic states. To say the least, uncertainty and so we stayed with the dry WPC fcst. && .AVIATION /21Z MONDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Conditions vary between MVFR and IFR late this afternoon as rain is spreading across the area. As the precipitation moves across the area, CIGS and VSBYS are expected to lower to IFR everywhere into this evening. Once the CIGS lower to IFR, they should remain so through the overnight hours. Conditions are expected to return to MVFR during the day Tuesday. Precipitation is expected to be mostly be rain, but occasional sleet or snow may mix in for ABE and RDG this evening and overnight. Winds continue to be gusty across the TAF sites, with ACY having the strongest winds of 45-50 knots. ILG, PHL, PNE, TTN could continue to see gusts 35-40 knots, while ABE and RDG could see gusts 30-35 knots. Winds will diminish some this evening, but gusts are expected to remain 20-30 knots through the overnight hours and into Tuesday. OUTLOOK... Tuesday night and Wednesday...VFR. NW winds 10-15 KT with gusts to 20 kt with winds backing to west in the afternoon. Late Wednesday night or Thursday...Isolated showers, possibly briefly lowering conditions to sub-VFR. Friday and Saturday...VFR. West winds 10-20 KT with gusts 25 to 30 kt.
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&& .MARINE...
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Storm Warning continues for the Atlantic Coastal Waters and Delaware Bay. Winds will diminish some this evening and overnight from south to north, so the Storm Warnings will likely be able to be downgraded to Gale Warning as the winds diminish. Gale force winds are then expected to remain during the overnight hours. Small Craft Advisory level winds are then expected on Tuesday. OUTLOOK... Tuesday night...northwest SCA, possible low end leftover gale early in the evening. Wednesday...Sub-SCA conditions expected. Thursday through Friday...West wind gusts 25-30 KT possible. Saturday...West wind gusts 20-25 knots possible.
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&& .HYDROLOGY... Flood Watch is in effect for this evening and tonight for central and NE NJ, where the flooding risk is highest (heaviest rainfall and most prone to flooding issues in urban locales). Impacts will be due to excessive rainfall, as between 1.5 and 2.0 inches of rain with locally higher amounts are expected from late this afternoon through tonight. No main stem river flooding is anticipated. However, minor flooding is possible along small streams and creeks and in areas of poor drainage. The entire region has some positive things working in its favor...precipitation has been below normal the last 30 days, there`s really no consequential snow cover to speak of, there`s no ice on area waterways, streamflows are either running at or below normal as is soil moisture, and last but not least, the ground isn`t frozen. We think all the above will help mitigate the flood threat especially for our counties outside the Flood Watch. && .TIDES/COASTAL FLOODING... A Coastal Flood Warning is in effect through Tuesday morning along the NJ and DE coasts and along Delaware Bay. Storm surge values of 3 to 4 feet are occurring. Fortunately, the astronomical tides are low and it should limit our region to widespread minor flooding with some areas of moderate flooding around the times of high tide late today and again on Tuesday morning. Strong wave action and the resulting beach erosion will likely compound the effects of the surge. Waves breaking along the shore may build to 6 to 10 feet. The expected surge along with the wave action and the forecast rainfall will likely result in additional and more widespread minor flooding around the high tide into this evening. We will keep the Coastal Flood Warning going for the tidal Delaware River and far upper Delaware Bay between New Castle County and Salem County for this evening`s high tide. The surge should lessen considerably there for Tuesday morning`s high tide based on the latest guidance. Based on the forecast guidance and the expected pattern we are not anticipating any coastal flooding on the upper eastern shore of Maryland. Also, the potential for anything more than spotty minor tidal flooding appears low for the tidal Delaware River above the Commodore Barry Bridge. The onshore flow is expected to begin backing toward the north tonight and to the northwest on Tuesday, lessing the threat for additional coastal flooding beyond Tuesday morning. && .CLIMATE... Rechecking monthly normal. The January departure at Philadelphia, when all is said and done, should end up 5 degrees above normal or 10th to 17th warmest January in the period of record. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Wind Advisory until 7 PM EST this evening for PAZ060>062-101- 103-105. High Wind Warning until 7 PM EST this evening for PAZ070-071- 102-104-106. Winter Weather Advisory until 11 AM EST Tuesday for PAZ054-055. NJ...Flood Watch through late tonight for NJZ008-010-012>015-020- 026. Wind Advisory until 7 PM EST this evening for NJZ007>010. Coastal Flood Warning until 11 AM EST Tuesday for NJZ012>014- 020>027. High Wind Warning until 7 PM EST this evening for NJZ015>019- 021. High Wind Warning until midnight EST tonight for NJZ012>014- 020-022>027. Coastal Flood Warning until 11 PM EST this evening for NJZ016. Winter Weather Advisory until 11 AM EST Tuesday for NJZ001. DE...Coastal Flood Warning until 11 AM EST Tuesday for DEZ002>004. High Wind Warning until 7 PM EST this evening for DEZ001-002. High Wind Warning until midnight EST tonight for DEZ003-004. Coastal Flood Warning until 11 PM EST this evening for DEZ001. MD...Wind Advisory until 7 PM EST this evening for MDZ008-012-015- 019-020. MARINE...Storm Warning until 1 AM EST Tuesday for ANZ452-453. Storm Warning until 4 AM EST Tuesday for ANZ450-451. Storm Warning until 10 PM EST this evening for ANZ430-431-454- 455. && $$ Synopsis...Drag Near Term...Robertson Short Term...Robertson Long Term...Drag Aviation...Drag/Robertson Marine...Drag/Robertson Hydrology...Staff Tides/Coastal Flooding...Staff Climate...Drag

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